This invention is directed generally to a mechanism for operating a hydraulic tool. More particularly, the present invention is directed to a mechanism employing a novel adjustment assembly for a hydraulic tool which allows the tool to be used with either a constant pressure hydraulic fluid system or a constant volume hydraulic fluid system without requiring disassembly or replacement of any parts in the tool.
Hydraulic tools generally operate using one of two basic types of hydraulic systems. The hydraulic systems which are used to operate such tools include the constant volume system and the constant pressure system.
In the constant volume system, the hydraulic fluid, such as oil, must be free to flow back to the power source in an off or neutral position. The constant volume system uses an on-off control valve arrangement which has an open-center spool to allow the hydraulic fluid to flow through the valve and back to the source when the valve is in its off or neutral position. As such, the terms “constant volume” and “open-center” are used interchangeably with respect to this type of system. In the open-center system, a positive displacement pump is used which continuously pumps hydraulic fluid through the system.
In the constant pressure system, the hydraulic pump operates only intermittently to achieve and maintain a desired pressure. A control valve associated with a constant pressure system employs a closed center spool to prevent fluid flow therethrough in the off or neutral position in order to maintain a desired system pressure. As such, the terms “constant pressure” and “closed-center” are used interchangeably. In the closed-center system, the system operates until a predetermined pressure is sensed whereupon the pump “destrokes” and the pressure compensated pump apparatus then operates to pump just enough to maintain the desired pressure. Various pumps or systems of this type are well known in the art.
Hydraulically driven tools are used in many applications in the field, for example, by utility companies for making crimp connections on power lines or by municipalities and park districts for operating pruning devices for tree management and maintaining landscaping. It should be understood that while the present invention is shown in connection with both a crimping device and a pruning device, the present invention will find applications in a variety of hydraulically operated tools.
Many of the foregoing users of such tools frequently employ both constant pressure type and constant volume type hydraulic power sources. For example, various equipment such as central hydraulic power sources or trucks which are used in the field, may be equipped with one or the other type of hydraulic power source. Typically, it is undesirable or economically restrictive to maintain both types of power sources in each field location. Without being able to know which type of hydraulic power source will be used in any particular field application, many users of such hydraulic tools found it necessary or desirable to maintain duplicate sets of tools in order to operate with either type of system. Providing duplicate sets of tools, however, represents a substantial capital investment as well as storage and maintenance costs even though it overcomes the problems associated with having only one type of hydraulic power system. Further, maintaining duplicate sets of tools requires additional space and additional training to make sure that the proper tool is used with the proper type of hydraulic system. Alternatively, one set of tools may be maintained in one type of hydraulic system selected for any given application. Some devices, such as trucks, however, are provided with only one type of hydraulic system and therefore this may not be a feasible solution.
Another way of solving the problems associated with the two different types of hydraulic power sources is to design tools with interchangeable components, such as two spool valves, one spool valve designed for open-center operation and the other spool valve designed for closed-center operations. The operator of the tool could then select and install the proper spool to match the hydraulic power source. This, however, would require that duplicate spools be available for use with each tool, again requiring additional inventory and storage costs as well as space requirements. Moreover, providing interchangeable spool valves would require the operator to expend the time necessary to effect the change over and also have sufficient training and skills to properly disassembly and reassembly the valve portion of each tool.
Assuming that the problems associated with inventory and storage costs and space requirements and operator skill and training are overcome, the dual valve spools require additional time at the job site for disassembly and reassembly of the valves. Another problem arises in that the frequent removal and replacement of the valve spools will also unnecessarily disturb the hydraulic system and seals and produce increased tool wear and the opportunity for the introduction of dirt and debris into the hydraulic system. Because these tools are intended for field applications, the introduction of such dirt and debris and disturbance of a hydraulic system is an important concern.
The invention disclosed in U.S. Pat. No. 3,882,883 proposed a first solution to the foregoing problems. The '883 patent discloses a valve assembly having a spool which may be rotated 180° to shift from a normally open operating mode to a normally closed operating mode. However, this valve design requires that a linkage rod be removed before the spool may be rotated. Thus, there is still the possibility of the linkage rod being improperly removed and improperly reassembled as well as possibly being lost, damaged during the removal or reassembly, or the introduction of contaminants into the system.
The invention disclosed in U.S. Pat. No. 4,548,229 proposed a second solution to the foregoing problems. The '229 patent discloses a valve assembly for accommodating both open-center and closed-center modes of operation for use with an impact wrench. This valve assembly, however, is suitable only for use with rotating tools, because the valve assembly itself is designed to shunt hydraulic fluid back to the source when the tool is in the off or neutral state, and the open-center mode of operation. This tool is provided with a specifically designed valve cylinder or sleeve which surrounds the valve spool. The sleeve is configured for open-center operation when in a first orientation and for closed-center operation when it is rotated to a second orientation approximately 180° of rotation from its first orientation. This valve is designed to permit constant flow of hydraulic fluid through the tool when the valve is in its on position in both open-center and closed center modes of operation. The valve is designed to cut off the hydraulic fluid flow at the valve itself in the closed center mode of operation when the valve is in its closed or neutral position. In other words, in both open-center and closed-center modes, when the valve is in its off or neutral position, the valve does not permit flow of fluid past the valve and there is no fluid flow to the tool. However, such a valve arrangement will not work with a reciprocating type of hydraulic tool wherein it is necessary to alternately direct flow to opposite sides of a reciprocating piston. The crimping device and the pruner disclosed herein in order to illustrate the present invention are two such types of tools which utilize a reciprocating piston, rather than a rotating rotor as used in the tools such as the impact wrench of the above-mentioned '229 patent.
The invention disclosed in U.S. Pat. No. 5,442,992 proposed a third solution to the foregoing problems. The '992 patent, which was assigned to the assignee of the present invention, shows a control system designed for use with either an open-center system or a closed-center system. The system of the '992 patent has a rotatable selector which assists in configuring the control system for use with either the open-center or closed-center system.
To overcome the disadvantages of the above-mentioned prior art, a hydraulic control mechanism was invented and disclosed in U.S. Pat. No. 5,778,755, which was assigned to the assignee of the present invention. The '755 patent discloses a hydraulic control mechanism which is attached to a hydraulically operated tool to provide a desired hydraulically powered function. The present invention allows the hydraulic control mechanism to be used with either an open-center hydraulic system or a closed-center hydraulic power system. The adjustment assembly, which utilized screws, provided a structure which could be configured to force open shuttle spool valves in the control mechanism in a neutral condition for use with an open-center power supply. The adjustment assembly can also be configured to be disengaged from the shuttle spool valves in a neutral condition for use with a closed-center hydraulic power supply. Operation of the adjustment assembly is made using standard tools and without disassembly of the control mechanism.
While the hydraulic control mechanism disclosed in the '755 patent has been well-received in the marketplace, there have also been some disadvantages associated therewith. For example, the adjustment of the screws was not convenient due to the location of the screws relative to a handle of the tool. Additionally, the components required for this method of adjustment occasionally led to fracture of the shuttle dump spools and external leakage. The number of parts required and costs to manufacture or purchase these parts, also resulted in higher manufacturing costs than desired.
Thus, there is a need for a mechanism for operating a hydraulic tool which overcomes the disadvantages associated with the prior art systems. The present invention provides such a mechanism.